524 research outputs found
Performance characterizations and thermodynamic analysis of magnesium sulfate-impregnated zeolite 13X and activated alumina composite sorbents for thermal energy storage
The composite sorbents of MgSO4-impregnated zeolite 13X and activated alumina are developed for thermal energy storage (TES) with different temperature ranges. The sorption and desorption characteristics of raw and MgSO4-impregnated activated alumina are studied, and the performances of the selected sorbents are tested in a closed-system TES device. The results are compared with those of raw and MgSO4-impregnated zeolite 13X. It is shown that the impregnated MgSO4 improves the overall TES performances of zeolite 13X and activated alumina. Compared to the raw host matrices, the impregnated MgSO4 remarkably accelerates the temperature-rising rate of zeolite 13X to about three times and improves the temperature lift of activated alumina by 32.5%. The experimental energy storage densities of MgSO4-impregnated zeolite 13X and activated alumina are 123.4 kWh m−3and 82.6 kWh m−3, respectively. The sorption temperature region of activated alumina is more aligned with the preferred hydration temperature of MgSO4 in comparison with zeolite 13X. The hydration characteristics of MgSO4 can resolve the solution leakage issue of open systems. Thermodynamic analysis is conducted to evaluate the performances of the TES device with different sorbents. It is found that entransy can be used to assess thermally and electrically driven TES systems reasonably
Vertical Confinement and Evolution of Reentrant Insulating Transition in the Fractional Quantum Hall Regime
We have observed an anomalous shift of the high field reentrant insulating
phases in a two-dimensional electron system (2DES) tightly confined within a
narrow GaAs/AlGaAs quantum well. Instead of the well-known transitions into the
high field insulating states centered around , the 2DES confined
within an 80\AA-wide quantum well exhibits the transition at .
Comparably large quantum lifetime of the 2DES in narrow well discounts the
effect of disorder and points to confinement as the primary driving force
behind the evolution of the reentrant transition.Comment: 5 pages, 4 figure
Two-Particle Correlation Functions for the 200-MeV 3-He + Ag Reaction
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
Spin-current modulation and square-wave transmission through periodically stubbed electron waveguides
Ballistic spin transport through waveguides, with symmetric or asymmetric
double stubs attached to them periodically, is studied systematically in the
presence of a weak spin-orbit coupling that makes the electrons precess. By an
appropriate choice of the waveguide length and of the stub parameters injected
spin-polarized electrons can be blocked completely and the transmission shows a
periodic and nearly square-type behavior, with values 1 and 0, with wide gaps
when only one mode is allowed to propagate in the waveguide. A similar behavior
is possible for a certain range of the stub parameters even when two-modes can
propagate in the waveguide and the conductance is doubled. Such a structure is
a good candidate for establishing a realistic spin transistor. A further
modulation of the spin current can be achieved by inserting defects in a
finite-number stub superlattice. Finite-temperature effects on the spin
conductance are also considered.Comment: 19 pages, 8 figure
Spin injection into a ballistic semiconductor microstructure
A theory of spin injection across a ballistic
ferromagnet-semiconductor-ferromagnet junction is developed for the Boltzmann
regime. Spin injection coefficient is suppressed by the Sharvin
resistance of the semiconductor , where is the
Fermi-surface cross-section. It competes with the diffusion resistances of the
ferromagnets , and in the absence of contact
barriers. Efficient spin injection can be ensured by contact barriers. Explicit
formulae for the junction resistance and the spin-valve effect are presented.Comment: 5 pages, 2 column REVTeX. Explicit prescription relating the results
of the ballistic and diffusive theories of spin injection is added. To this
end, some notations are changed. Three references added, typos correcte
Sensitivity of deexcitation energies of superdeformed secondary minima to the density dependence of symmetry energy with the relativistic mean-field theory
The relationship between deexcitation energies of superdeformed secondary
minima relative to ground states and the density dependence of the symmetry
energy is investigated for heavy nuclei using the relativistic mean field (RMF)
model. It is shown that the deexcitation energies of superdeformed secondary
minima are sensitive to differences in the symmetry energy that are mimicked by
the isoscalar-isovector coupling included in the model. With deliberate
investigations on a few Hg isotopes that have data of deexcitation energies, we
find that the description for the deexcitation energies can be improved due to
the softening of the symmetry energy. Further, we have investigated
deexcitation energies of odd-odd heavy nuclei that are nearly independent of
pairing correlations, and have discussed the possible extraction of the
constraint on the density dependence of the symmetry energy with the
measurement of deexcitation energies of these nuclei.Comment: 14 pages, 3 figure
Bloom-Gilman duality of inelastic structure functions in nucleon and nuclei
The Bloom-Gilman local duality of the inelastic structure function of the
proton, the deuteron and light complex nuclei is investigated using available
experimental data in the squared four-momentum transfer range from 0.3 to 5
(GeV/c)**2. The results of our analysis suggest that the onset of the
Bloom-Gilman local duality is anticipated in complex nuclei with respect to the
case of the protonand the deuteron. A possible interpretation of this result in
terms of a rescaling effect is discussed with particular emphasis to the
possibility of reproducing the damping of the nucleon-resonance transitions
observed in recent electroproduction data off nuclei.Comment: revised version, to appear in Physical Review
Measurements of the Mass and Full-Width of the Meson
In a sample of 58 million events collected with the BES II detector,
the process J/ is observed in five different decay
channels: , , (with ), (with
) and . From a combined fit of all five
channels, we determine the mass and full-width of to be
MeV/ and
MeV/.Comment: 9 pages, 2 figures and 4 table. Submitted to Phys. Lett.
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